The goal of this K24 is to provide salary support for Dr. Singh to allow him to spend 40% of his time mentoring pulmonary and critical care fellows, junior faculty and other trainees in patient-oriented research on chronic airway infections. This proposal will enable Dr. Singh to expand his translational research program, integrate fellows and junior faculty in to the program, and provide protected time so that the can mentor additional MD fellows. The proposal also provides time and infrastructure to help Dr. Singh enhance his own mentoring skills. The two research projects described involve face-to-face interactions with patients Project 1 exploits preliminary findings which show that infecting P. aeruginosa strains evolve to produce genetically diverse but clonally-related populations within CF lungs, and that the relative abundance of subpopulations change as patients are treated with antibiotics. This is important because subpopulations that increase during treatment have phenotypes that enable them to resist treatment in vivo, while those that decrease lack resistance functions. Studying these subpopulations enable us to test novel hypotheses about the mechanisms enabling bacteria to withstand antibiotics in chronic infections. Project 2 exploits preliminary findings that show that upper airway contamination may confound DNA-based measurements of lung microbiota. Accurately identifying the bacteria causing CF infections is among the most important tasks in CF infection research. We propose using the novel 2-scope method, along with advanced analytic methods, to test the hypotheses that some of the taxa identified in upper airway samples from CF children using DNA-based methods are oropharyngeal contaminants, or are derived from non viable cells.